DESCRIPTION: Studying the photocycle of halo rhodopsin, a chloride pump, with FTIR as well as FT visible and FT Raman. Renewal request of a previous 3 year award, now back to BBCA as an amended proposal. Specific aims are to resolve the photocycle of hR. Examine whether or not the Schiff base frequency is halide dependent and whether or not bands from the arginine side groups are also halide dependent. Then, try to identify which args are those showing up in the IR difference spectrum. One last goal is to obtain IR difference spectra in response to, with and without halide salts in solution, using an ATR cell and flowing the ions. A new faster (5 microsecond) FT-IR spectrometer has just been installed. This will provide about three orders of magnitude better resolution.